Deposition of environmental tobacco smoke (ETS) in the lung depends upon the distributions of the various components between the vapor and particle phases and upon the particle-size distribution. In order to understand the relationships between exposure of non-smokers to ETS and their dose, it is necessary to understand how the fundamental physical and chemical properties of ETS differ from those of mainstream tobacco smoke. We propose a program of research to determine the vapor-particle partitioning and particle-size distributions of polycyclic aromatic hydrocarbons (PAH) and tobacco-specific N-nitrosamines (TSN) and their precursor alkaloids, including nicotine, in ETS for a range of environmental conditions of dilution, lighting, aging, relative humidity and temperature. The PAH and TSN fractions are suspected to play a significant role in the overall carcinogenic properties of tobacco smoke (Hoffmann and Wynder, 1986). The objectives of the proposed research are: 1. To develop sampling methods to effectively separate and collect vapor and particulate phases of selected components of ETS and to characterize the chemical composition of ETS as a function to particle size; 2. To characterize the vapor-particle and particle-size distributions of selected ETS components under different conditions of dilution, lighting, temperature, relative humidity and aging; 3. To compare measured and modeled dynamics of particle-size distributions and of vapor-particle partitioning as functions of dilution, lighting, temperature, relative humidity and aging of ETS, and 4. To investigate reactions of amines with NO(x), and HNO(x) to form tobacco-specific N-nitrosamines. Experiments will be conducted in a special Environmental Chamber in which dilution, aging, temperature and relative humidity are controlled. Aerosol models will be used to interpret the experimental measurements of the dynamics of vapor-particle partitioning and particle-size distributions.